A conventional cathode ray tube (CRT) is equipped with an electron gun for energizing and illuminating a presentation screen. The electron gun includes a heated filament therein for emitting electrons, which will then eventually travel to the screen. Conventional CRTs also include some type of a focusing mechanism to concentrate the emitted electrons into an electron beam and a deflection mechanism to direct the electron beam to the presentation screen. The presentation screen comprises a plurality of pixels or phosphor dots,, which are arranged in rows across the screen. In color television sets, each pixel includes red, blue and green phosphor dots; in black and white television sets, there is in effect one phosphor dot per pixel. The deflection mechanism directs the electron beam from one pixel to the next, illuminating each pixel individually in a row by row manner. In this way, the entire screen is scanned by the beam to produce an image.
The quality of a dynamic video image shown on the presentation screen is affected by how rapidly the electron beam can scan the screen. A higher quality dynamic video image will be produced when scanning is rapid. However, the scanning speed in conventional CRTs is limited because the electron beam must travel long distances across the presentation screen during each scan. Moreover, the scanning speed in conventional CRTs is limited because the electron bean must be focused on each pixel for a certain "dwell" time period to impart sufficient energy to properly illuminate the phosphor dot.
Further, a typical raster-type CRT requires a great deal of current so that each of the phosphor dots on the CRT screen will be appropriately energized during the dwell time. If individual electron beams could be used to illuminate phosphor dots, the current for each of the electron beams could be much less. Further, the dynamic response of the CRT could be improved if these multiple beams could be independently modulated in intensity.
Thus, a need has arisen for a cathode ray tube that does not require the scanning of the presentation screen by an electron beam to produce visual images.